1. Field of the Invention
The present invention relates to a compressor. In particular the present invention relates to an apparatus and a method for accurately controlling operation of a reciprocating compressor by reducing a stroke estimation error of a reciprocating compressor.
2. Description of the Prior Art
FIG. 1 is a block diagram illustrating a construction of an operation control apparatus of a reciprocating compressor in accordance with the conventional art.
As depicted in FIG. 1, the operation control apparatus of the reciprocating compressor includes a current detector 4 for detecting current applied to a motor (not shown) of a reciprocating compressor 6; a voltage detector 3 for detecting a voltage applied to the motor; a stroke calculator 5 for calculating a stroke estimation value of the compressor 6 on the basis of the detected current, voltage and parameters of the motor; a comparator 1 for comparing the calculated stroke estimation value with a preset stroke reference value and outputting a difference value according to the comparison result; and a stroke controller 2 for controlling a stroke of the compressor 6 by varying a voltage applied to the motor in accordance with the difference value. Hereinafter, the operation of the operation control apparatus of the reciprocating compressor will be described.
First, the current detector 4 detects current applied to the motor of the compressor 6 and outputs the detected current to the stroke calculator 5. Also, the voltage detector 3 detects a voltage applied to the motor and outputs the detected voltage value to the stroke calculator 5.
The stroke calculator 5 calculates a stroke estimation value of the compressor with Equation 1 by substituting the detected current value, the detected voltage value and the parameters of the motor and applies the calculated stroke estimation value to the comparator 1.                     X        =                              1            α                    ⁢                      ∫                                          (                                                      V                    M                                    -                                      R                    ⁢                                          xe2x80x83                                        ⁢                    i                                    -                                      L                    ⁢                                          xe2x80x83                                        ⁢                                          i                      _                                                                      )                            ⁢                              ⅆ                t                                                                        Equation        ⁢                  xe2x80x83                ⁢        1            
where R is resistance, L is inductance, xcex1 is a motor constant, VM is a voltage applied to the motor, i is current applied to the motor, and {overscore (i)} is a time variation rate of current applied to the motor. In particular, {overscore (i)} is a differential value (di/dt) of i.
Afterward, the comparator 1 compares the stroke estimation value with the stroke reference value and applies a difference value according to the comparison result to the stroke controller 2.
The stroke controller 2 controls a stroke by varying the voltage applied to the motor of the compressor 6 on the basis of the difference value, It will be described in detail with reference to accompanying FIG. 2.
FIG. 2 is a flow chart illustrating an operation control method of the reciprocating compressor in accordance with the conventional art.
First, when a stroke estimation value is applied from the stroke calculator 5 to the comparator 1 as shown at step S1, the comparator 1 compares the stroke estimation value with a stroke reference value and outputs a difference value according to the comparison result to the stroke controller 2 as shown at step S2.
When the stroke estimation value is less than the stroke reference value (S2, YES), the stroke controller 2 increases a voltage applied to the motor in order to control a stroke of the compressor 6 as shown at step S3. On the other hand, when the stroke estimation value is greater than the stroke reference value (S2, NO), the stroke controller 2 decreases a voltage applied to the motor as shown at step S4.
As described above, in the apparatus and the method for controlling operation of the reciprocating compressor in accordance with the conventional art, a stroke estimation value is calculated by using parameters (motor constant, resistance, inductance) of the motor, and a stroke of the compressor is controlled on the basis of the calculated stroke estimation value. Accordingly, an error in the calculated stroke estimation value can increase due to deviation of the parameters of the motor (in particular, resistance and inductance) from the standard values and due to non-linearity.
In addition, in the apparatus and the method for controlling operation of the reciprocating compressor in accordance with the conventional art, because an error in the calculated stroke estimation value can be large, it is impossible to control operation of the compressor accurately or precisely.
In order to solve the above-mentioned problem, it is an object of the present invention to provide an apparatus and a method for controlling operation of a compressor capable of greatly decreasing an error in a stroke estimation value of a compressor by comparing a first stroke estimation value calculated on the basis of a current, a voltage applied to a motor of the compressor and parameters of the motor with a second stroke estimation value calculated on the basis of a counter electromotive force.
It is another object of the present invention to provide an apparatus and a method for controlling operation of a compressor capable of controlling operation of a compressor accurately and precisely by compensating a preset stroke reference value on the basis of a first stroke estimation value and a second stroke estimation value, comparing the compensated stroke reference value with the first stroke estimation value and controlling operation of the compressor according to the comparison result.
In order to achieve the above-mentioned object, a method for controlling operation of a compressor in accordance with the present invention includes calculating a first stroke estimation value of a compressor on the basis of a current, a voltage applied to a motor of a compressor and preset parameters of the motor; detecting a counter electromotive force of the motor; calculating a second stroke estimation value of the compressor on the basis of the detected counter electromotive force value; determining a new stroke reference value by comparing the first stroke estimation value with the second stroke estimation value, adding or subtracting a stroke compensation value corresponding to the comparison result to or from a preset stroke reference value; and controlling a stroke of the compressor by varying a voltage applied to the motor on the basis of the determined stroke reference value and the first stroke estimation value.
In order to achieve the above-mentioned object, an apparatus for controlling operation of a compressor in accordance with the present invention includes a detector for detecting a current and a voltage applied to a motor of a compressor; a first stroke calculator for calculating a first stroke estimation value of the compressor on the basis of the detected current value, voltage value and preset parameters of the motor; a counter electromotive force detector for detecting a counter electromotive force of the motor; a second stroke calculator for calculating a second stroke estimation value of the compressor on the basis of the counter electromotive force; a stroke compensation value calculator for calculating a stroke compensation value on the basis of the first stroke estimation value and the second stroke estimation value; a stroke reference value determiner for adding or subtracting the stroke compensation value to or from a preset stroke reference value and determining the added or subtracted stroke reference value as a new stroke reference value; and a stroke controller for controlling a stroke of the compressor by varying a voltage applied to the motor on the basis of the first stroke estimation value and the determined stroke reference value,